On Wed, Aug 13, 2014 at 9:51 AM, Stephen Warren [off-list ref] wrote:

On 08/13/2014 02:53 AM, Thierry Reding wrote:

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On Tue, Aug 12, 2014 at 06:56:07PM -0700, Dylan Reid wrote:

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The Acer Chromebook 13, codenamed "Big", contains an NVIDIA tegra124
processor and is similar to the Venice2 reference platform.

The keyboard, USB 2, audio, HDMI, sdcard and emmc have been tested
and work on the 1366x768 models.  I haven't tried on the HD systems
yet.

Presumably the HD systems will have a different compatible? Is it only
the panel that's different or are there other changes?

Yes, we definitely need to plan ahead for the different SKUs. I assume we'll
have different board names for each board, which then translates int DT
filenames and U-Boot/cbootimage-configs/tegra-uboot-flasher board

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There is also an issue on reboot because the TPM isn't reset.  It will
cause the stock firmware to enter recovery mode.  This can be worked
around by an EC-reset, press refresh and power at the same time.

It's not clear to me what exactly this implies. Does it mean the system
won't boot unless you manually press "refresh" and "power"? Are those
keyboard buttons or keys on some debug board?

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diff --git a/arch/arm/boot/dts/tegra124-big.dts

b/arch/arm/boot/dts/tegra124-big.dts

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+/ {
+       model = "Google Big";

Perhaps this should at least mention that it's the Acer Chromebook 13.
Otherwise this could just as well be some random development board.

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+       compatible = "google,nyan-big", "nvidia,tegra124";

What's "nyan"? Are there other variants of "big" other than "nyan"?

I thought this board was known as Nike?

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+       pinmux: pinmux at 0,70000868 {
+               pinctrl-names = "default";
+               pinctrl-0 = <&pinmux_default>;
+
+               pinmux_default: common {
+                       dap_mclk1_pw4 {
+                               nvidia,pins = "dap_mclk1_pw4";
+                               nvidia,function = "extperiph1";
+                               nvidia,enable-input =
<TEGRA_PIN_DISABLE>;
+                               nvidia,pull = <TEGRA_PIN_PULL_NONE>;
+                               nvidia,tristate = <TEGRA_PIN_DISABLE>;
+                       };

Stephen proposed a patch not so long ago that removes the static pinmux
settings from DTS files[0]. I'd expect he'll have objections to this DTS
providing the static settings.

The assumption with that patch is that the bootloader will have to set
up the entire pinmux anyway (to prevent conflicting settings), therefore
there'd be no need to do it in the kernel. Is this something that your
bootloader already does (or could be modified to do)?

[0]: http://patchwork.ozlabs.org/patch/363222/

Yes, definitely I want to remove the pinmux from the kernel, since the HW
design implies that the bootloader must set this up completely.

IIRC, the bootloader on this device doesn't. However, the workaround was
that the U-Boot that the firmware chain-loads in order to load Linux (which
IIRC is mandatory for non-Google kernels?) would do this setup before
booting the kernel.

You can wrap a regular mainline kernel with the verified boot block
and load it without u-boot. I do it all the time on x86, ARM is no
different.

The main reason for using u-boot is so that you get a command line,
can do network-based booting, bootloader configuration scripts, and so
on.

So, it's not a useful workaround, unfortunately. :(


-Olof